Method of operating metallurgical furnaces



nited States Patent 3,218,155 METHOD OF OPERATING METALLURGICAL FURNACESJulius H. Strassburger, Coraopolis, Pa., assignor to National SteelCorporation, a corporation of Delaware No Drawing. Filed Dec. 22, 1960,Ser. No. 77,507 23 Claims. (Cl. 7542) This application is acontinuation-in-part of Serial No. 54,366, filed September 7, 1960, andnow abandoned.

This invention relates to blast furnaces and more particularly toimprovements in the method of operating blast furnaces.

Conventional blast furnaces comprise a hearth, a stack and bosh betweenthe hearth and the stack. The blast, comprising essentially compressedair, is blown through tuyeres mounted in the bosh into the upper portionof the hearth, and the burden, including specific proportions oflimestone, ferrous bearing material and carbonaceous material is chargedinto the furnace at the top of the stack. The ferrous bearing materialis usually iron ore and may include some scrap metal, sinter or othermaterial and the carbonaceous material is usually coke. The charge movesdown the shaft of the furnace and when it reaches a zone adjacent thetuyeres the coke is burned by the incoming blast to melt the iron oreproducing molten pig iron and the hot gaseous products of combustionflow up through the stack, preheating the descending charge and reducingthe iron ore as it approaches the combustion zone, and out through thetop of the furnace.

The quantity and physical character of material discharged into the topof the furnace as burden and the volume of blast gas blown into thefurnace are calculated and controlled to maintain the highest possiblerate of pig iron production with minimum coke consumption and withminimum flue dust production. The volume of blast gas required dependsupon the physical characteristics of the furnace and the components ofthe burden and must be carefully controlled in order to maintain asmooth operating furnace. It is known that an insufiicient volume ofblast gas results in low pig iron production and high coke rates, whileexcessive blast gas increases flue dust production without acorresponding rise in iron production.

The driving rate of a blast furnace is a measure of the quantity ofcarbon gasified at the tuyeres by combustion of coke. Since cokecombustion is influenced by the oxygen available and by the existingtemperature it has been proposed in the past to increase the productionof blast furnaces without substantially increasing the volume of blastgas by either enriching the blast gas with oxygen or by blowing theblast gas to the furnace at an elevated temperature. It was foundhowever that the mere enrichment of the blast gas with oxygen or themere increase in temperature of the blast gas did not produce theexpected results as the furnace either ran cold due to resulting highvelocity of upwardly flowing bosh gas or that the movement of the burdenslowed down and became intermittent or at times actually stopped andcaused the furnace to hang which was followed by violent slips. It wastheorized that the inability to obtain a smooth operating furnace whenenriching the blast gas with oxygen or by elevating the temperature ofthe blast gas results from the fact that oxygen enrichment of the blastgas or increase in blast gas temperature produces more intensifiedburning of the coke and thereby shortens the combustion zones in frontof the tuyeres, and that reducing the size of the combustion zonesenlarges the mass of burden centrally positioned with respect to thehearth and decreases the area available for upward flow of combustiongases. It was then discovered that the addition of moisture to the blastgas made it possible to obtain a smooth operating furnace when enrichingthe blast gas with oxygen or when blowing the blast gas at an elevatedtemperature. The addition of moisture or its equivalent to blast gasmakes it possible to enrich the blast gas with oxygen or to blow theblast gas at a higher temperature and thereby improve furnaceproduction. While added moisture comprises a cheap source of oxygenwhich is introduced into the furnace without nitrogen and also providesa source of hydrogen gas which is more eflicient than carbon monoxide inreducing iron ore, higher rates of iron production would be obtained ifit were possible to reduce the quantity of moisture required sincedisassociation of water is an endothermic reaction absorbing heat fromthe combustion zone and since the coke rate is proportional to thetemperature.

It is well known that blast furnaces may be operated to produce, withinlimits, products of specified characteristics and it is desirable toobtain smooth operations in blast furnaces producing pig iron ofdifferent chemical compositions, temperatures, etc. Accordingly, theobtaining of a smooth operating furnace by means of moisture additionsto the blast gas includes the feature of controlling the characteristicsof the product by such moisture additions.

It is, therefore, a principal object of the present invention to providea novel method of operating a blast furnace by which maximum ironproduction is obtained with a minimum coke rate.

Another object is to provide a novel method of operating a blast furnaceby which combustion of coke is intensified without correspondinglyincreasing the volume of blast gas in such a manner as to requireminimum moisture additions to the blast gas.

It has been established that predetermined quantities of moisture arerequired to be added to oxygen enrichedv blast gas or to blast gas at anelevated temperature in order to obtain smooth operating furnaces. Thequantity of moisture required may be considered as depending for themost part upon the percentage of oxygen enrichment or upon the blasttemperature although the moisture actually required may be influenced bythe physical characteristics of the furnace or by the constituents ofthe burden. In particular, the in blast gas at about 1100 oxygenenrichment is shown in Table I.

TABLE I quantity of moisture required Moisture in blast (grains Oxygenenrichment (percent): per cubic foot) It has also been established thatunder average conditions about 2.5 to 3.5 grains of moisture percubicfootof blast gas is required to maintain a smooth operating furnace whenblown with blast gas at a temperature of about 1100 F. Without oxygenenrichment, and that about 1 grain of moisture per cubic foot of blastgas is required to be added to the blast gas upon each 30 F. increase ofthe blast gas temperature. From the foregoing, it 'is possible toascertain the quantity of moisture that would be expected to benecessary in blast gas at varying temperatures and at variouspercentages of oxygen enrichment in order to obtain a smooth operatingfurnace. Tables II through XI disclose the range of moisture requiredthroughout a blast temperature range F. for varying percentages of TABLEX.4.5% OXYGEN ENRICHMENT It was believed in the past that the quantityof moisture required in blast gas for maintaining a smoothly op- Bl tT tMgisgure expecged Moisturgrequjred crating furnace is a function of thepercentage of oxygen as empera ure erequire accor ing to R 1 (grains percubic foot) present invention enr1chment and of the blast gastemperature and that (grams per oubictoot) 5 the total molsture requiredis, for all practical purposes, a summation of the moisture necessaryfor the oxygen g :8 3 E8 3 enrichment and the moisture necessary for theblast gas 21, 21,51 0 311 temperature. Tables 11 through XI, under theheading 3;; 3 3%: 3 31332221 Moisture expected to be required, discloseranges of gig i 3 g 23-; mo1sture requ1red for d1iferent percentages ofoxygen O 38,1 to 48,1 341 to 44,1 enrichment and blast gas temperaturesaccording to this i 2 2g 2;; 25-2 g3? prior understanding of blastfurnace operation. gagto 28g 44I0to 5410 It has been determined fromobserving actual furnace 1. to 1. 47.3t0 57.3 6M we to m 6 15 operationsthat unexpected advantages are reahzed by 57-910 to utlhzing blast gasheated to a temperature above a critlcal 61. 2 to 71. 2 57. 2 to 67. 2

range. In particular 1t has been dlscovered that blast furnaces blownwith blast gas heated to temperatures below TABLE OXYGEN ENRICHMENT 1400F. require a moisture content that falls within the M t d d expectedranges, while with blast gas heated to temperaois ure expeete Moisturerequire c 6 Blast Temperature F0 be requiged accorqing tq tures aboveabout 1400 1 .4500 F. the quant1ty of o ains per cu l f P e gu gmoisture required to mamtain a smooth operating furnace grams per cu 1c00 is substantially less than the minimum moisture that would 17 toy/817 to 28 be expected to be requ1red according to the prior underto tostanding of blast furnace operations. 1 1 In Table XII, Examples A, B,C, D, and Bare a tabulagg'fl i -g gg-gz 2g? t1on of data obtained whenoperating 1dent1cal furnaces O 0 36.8to 47.8 32.8t0 43.8 having a hearthd1ameter of 28 feet and a height of 108 40.1 to 51.1 36.1 to 47.1 v 43L4 to 54. 4 4 to 50. 4 30 feet without o ygen enrichment. Examples Fthrough 46. 7 t 57.7 42.7 t 53.7 N are a tabulation of data obtamed whenoperatmg ldenggjggg 21 2 2321325 3 tical furnaces having a hearthdiameter of 25 feet, 6 5&6, 526106315 inches, a height of 100 feet and aworking volume stock 59. 9 to 70. 9 55. 9 to 66. 9 h 63.2t0 74.2 59.2to70.2 lme to center lme of tuyeres of 37,872 cubic feet wit oxygenenrichment. The data given are averages of values obtained during theperiod of operation indicated.

TABLE XII Example A Example B Example 0 Example D Example E Example FExample G Iron Prod. Net Tons Per Day 1, 499 1, 958 2, 236 1 963 2 3011, 501 1, 613 Iron Piotr: Net Tons Per Day S.F 1, 499 1,870 2,122 1196321181 1, 489 1, 606 goke Raige, 112211? Net Ton SJ 1, 602 1, 250 1, 2701, 3 1, 270 1,163? 1,263: X en 11110 en Wi Blown, 0.1.111 78,460 92,14997,169 105, 521 101, 080 75,100 74,900 ll d l 6 Ft 11 8 17 3 187; 14 172ib i5 gg 1: ins e u. 015 m r 31. 6 58.9 61.4 59.9 52.2 16. g 24. g 6. 913. 38 2' 33. 2 39 4 1 0 11.

52 5 Blast Tem erature 1 277 1,602 1 641 1 654 1 673 1 260 1 285 TopTemp rature, 271 304 301 264 278 30 295 Stone Rate, Lbs. Per Net 553 442337 599 539 715 667 Dust Rate, Lbs. Per Net Ton S F 214 146 261 128 182190 193 Burden, Lbs. Per Charge--- 28, 626 76, 493 80,102 75, 033 78,072 25, 703 27, 093 Charges Per Day 188 92 95 103 206. 5 211. 9 Delays,Minutes Per Day- 54 44 91 38 26.3 29. 5 Days Operated 31 31 29 30 31 3131 Slag Volume, Lbs. Per Net To 848 846 (JO/CO Ratio- 1. 83 1. 76

Example H Example I Example I Example K Example L Example M Example NIron Prod. Net Tons Per Day 1 596 1 582 1 820 1,601 1,685 1 720 1 822Iron Prod Net Tons Per Day S.F 1: 596 1: 582 11 812 1, 597 1, 685 1: 7201: 822 Coke Rate, Lbs. Per Net Ton S.F 1, 574 1, 642 1, 342 1, 652 1,619 1, 591 1, 505 Oxygen Enrichment 3. 03 3. 54 1. 49 3.01 4.0 4.00 r)4. 0 Wind Blown, 0.1m 72,800 73,000 75,200 73,000 72, 900 72,900 7-,900Equivalent Wind, e.f.m ,300 85, 300 80, 500 83, 500 86,900 86,900 86,900Moisture, Grains Per Cu. Ft 16, 82 21.37 11. 92 20.01 23.88 23.96 24.15Sinter, percent 36.3 36. 6 66. 6 24. 6 37. 5 40. 4 50.0 Lima in Sinter,percent- 8-10 8 8 8 8 9 8 8 Oversize, percent 12.8 12. 8 19. 9 10.8 12.7 1-. 7 12. 7 Fe in Burden, percent. 54. 58 54.60 56. 08 54.19 54. 6554. 84 55. 34 Blast; Temperature, F 1, 305 1, 375 1, 425 1, 540 1, 5651, 570 1, 580 Top Temperature, F 265 260 305 260 235 240 261 Stone Rate,Lbs. Per Net Ton S.F 672 742 387 778 766 733 643 Dust Rate, Lbs. Per NetTon S.F 127 112 104 139 111 104 84 Burden, Lbs. Per Charge 27,899 27,42344,612 27,250 27,166 27,381 28, 000 Charges Per Day 196. 5 202. 2 134. 7203. 5 216. 8 216. 2 214. 3 Delays, Minutes P Day 27.7 27.8 17. 5 30.328. 7 28.4 27. 5 Days OperatetL. 31 30 30 31 23 31 8 Slag Volume, Lb 900939 762 920 950 933 872 CO/COZ Ratio 1.80 1.83 1.76 1.72 1. 72 1. 71

3,2 1 a, i 5 s 3 8 TAB LE X111 Blast E nric'ued Actual Moisture Tcmpera-O xygeu, Moisture Expected Moisture ture, F. Percent (grains per grainspct Saving cubic loot) cubic foot) Example A..- 1, 277 11.8 11. 8 0Example B 1, 602 0 17. 3 22. ii 5. 3 Example C 1, 641 0 1S. 23. 9 5. 3Example D 1, 654 0 14. 0 24. 4 10. 0 Example E 1, G73 0 1T. 2 25. 0 7. 8Example F 1, 200 1t 65 10. 7 .3 3i 3 0 Example G 1, 235 2. 98 15. SS 2l3 0 Example H 1, 305 3. 03 10. 82 t. 1 6 0 Example I..- 1, 37:3 3. 5121. 37 1-28.1 0

1, 425 1. 49 11. 92 1 1S.4 2. 8 1, 5-10 3. 01 20. ()1 5 33. 53 52 1, 5554. 0 23. 7. 3 4. 4S 1, 570 i. 0 23. 00 i7. 53 4. 57 l. 580 4. 0 2 15 13T. 85 4. T1

Table XIII is a comparison of moisture content of the blast gas inExamples A through N with the moisture content that would be expected tobe required according to Table I for oxygen enrichment and in accordancewith general rule of adding 1 grain of moisture for each F. increase inblast gas temperature- From Table XIII, it is seen that with blast gastemperatures at and below 1375 F. the total moisture actually used inthe blast gas in order to maintain a smoothly operating furnace fallsroughly within the range of Moisture expected to be required, while withblast gas temperatures of about 1400 to 1500" F., and above, themoisture actually needed for maintaining a smoothly operating furnace isabout four grains or more of moisture per cubic foot ofblast gas lessthan the minimum moisture content expected to be required. Thus,according to the principles of the present invention by blowing blastgas heated to a temperature above 1400 F. and/ or enriched with oxygenit is possible to reduce the quantity of moisture in the blast gas by atleast four grains per cubic foot of blast gas as compared to the totalmoisture believed to be necessary. A reduction of four grains ofmoisture in the blast gas blown to the furnace makes it possible toincrease the blast gas temperature by at least 120 F. Without additionalmoisture, as a result the coke consumed per ton of iron produceddecreases by the order of to pounds with a corresponding increase in pigiron production. From a comparison of Examples I, J, and K, for theparticular blast furnace producing these operational examples, itappears that the critical blast gas temperatures above which theunexpected saving in required moisture is obtained is probably around1425 F. to 1450 F. However, since blast furnace performance depends uponphysical characteristics of the blast furnace and upon variable factorsincluding composition of the burden and physical characteristics ofconstituents of the burden it is believed the critical temperature foraverage blast furnace installations falls within the range of about 1400F. to 1500 F., that is, with blast gas heated to a temperature aboveabout 1400 F. to 1500 F. unexpected savings in required moisture can berealized.

While it is not known precisely why the blowing to a blast furnace ofblast gas heated to temperature above about 1400 F. to 1500 F. makes itpossible to reduce the moisture required in order to obtain a smoothlyoperating furnace, it is believed that blast gas temperatures above thecritical temperature have some effect upon the combustion zones in frontof the tuyeres to reduce the size of the core of substantially solidmaterial in the region of the center of the hearth thus permittingcombustion gases to flow more easily upwardly into the stack. it is alsopossible, but not known as a matter of fact, that the use of oxygenenrichment, which increases the oxygen contact per cubic foot of blastgas while actually decreasing the volume of the blast gas, may have someeffect to compensate for the disadvantages resulting from expansion ofblast gas with increasing temperature when theblast gas temperature isabove the critical temperature of about 1400 F. to 1500" F. Although itcannot be said definitely why the combination of oxygen enrichment andelevated blast gas temperatures above about 1400 F. to 1500 F. resultsin a reduction in the moisture required in order to obtain a smoothlyoperating furnace, observations of furnaces in actual operationdemonstrate that the unexpected results are obtained.

Tables 11 through XI include the range of moisture required according tothe principles of the present invention for various ox gen enrichmentpercentages at blast gas temperatures. It will be noted that with blastgas temperatures below 1400 F., the moisture required according to thepresent invention is similar to the moisture expected to be required,while at blast gas temperatures above 1500 F. the range of moisturerequired according to the present invention is about four grains percubic foot less than the moisture expected to be required for similarpercentages of oxygen enrichment and blast gas temperatures. Althoughthe examples in Table XII show moisture savings greater than four grainsper cubic foot of blast gas can be obtained with some furnaces at highblast gas temperatures and although moisture savings should increasewith increasing blast gas temperatures, for the sake of clarity, theranges of required moisture according to the present invention as setforth in Tables 11 through XI are based on minimum savings of fourgrains of moisture per cubic foot of blast gas.

Blast furnaces in existence today are generally capable of operationwith blast gas temperatures as high as about 2000 F. providingsufiicient stove capacity is available. For operation with blast gastemperatures above 2000 5., it will be necessary to utilize hightemperature materials in the construction of certain components of thefurnace. Although operation'with blast gas temperatures above 2000 F. isplanned and high temperature materials necessary forsuch operation areeither in existence or under development, the practical range of blastgas temperatures according to the present invention is from about 1400F. to 1500 F. and up to about 2000 F. Inasmuch as the. quantity ofmoisture saved by practicing the present invention is believed toincrease with increasing blast gas temperatures, and since moreefiicient overall operation will be obtained when it is possible tooperate blast furnaces with higher blast gas temperatures, the operationrange of blast gas temperatures extends also from about 2000 P. to 2500F.

10 Table XV is a composite of data on moisture required in accordancewith the invention taken from earlier in view of the present lack of Aswill be described in more detail in It is seen from Table XIV thatfurnace efiiciency tion the practical range of oxygen enrichment is Theteachings of the present invention are applicable,

without oxygen enrichment and without moisture addition.

creases as the percentage of oxygen enrichment increases. However, atthe present time it is not economical to operate furnaces with oxygenenrichment of the order of 10%, for example,

facilities of oxygen producing equipment of the necessary capacity.Accordingly, for practicing the present inven from about 1% to while thepreferred range is from about 5% to with or without oxygen enrichment,no matter how moisture or its control equivalent is added to thefurnace. For example, it has been discovered that the high blasttemperatures taught by the invention permit, in fact, actually arerequired for, auxiliary fuel additions to the blast furnace.

subsequent paragraphs, these auxiliary fuels have many of the sameelfects thermodynamically as aqueous additions and for many purposes canbe considered control equivalents. The teachings of the inventioninclude methgrains Although this table TABLE XIV .5% TO 10% OXYGENENRICHMEN'I Table XIV discloses calculated av r S b .m mm Mm mm m m m mi m F 01 V1 3 t r moaebe t a f .lh C H O 0 1 r. 0 C F m e 0 m m% S S Hmm a H 1 1 t g0 n 1 e 1 n 6 O 6 1 h f fl g t T O n O I 0 a m 6 S ek .1 fm t 0 5 r r 6 S V S 0 G H O a .11 a D.H 3 .ud r eue d e mm md fln H I q6 m :1 e I e m a S 6 O m 25814703692 m m nm mawpm t d d .1.Ho a C 700000000000 nenv. O f lO N O ttttttttttt a H 310 S P f. g 0 m 0 125814703692 u a M m fm n l e I m .aaaaaaaaasa S e m H O 0.1 0 6 f T 5.22333444555 Ii d 6 e t e t eh N o u t S a a X m t m m w e I w t S a E umm xbww m dv V m m m 0 3 gm 0 O S H a N 25814703692 a I m m w th w t e wyd a m T swcamammeam nmmu mwasvmww s L 5 w 0 Nud 8 S g N mmtwmmm twmtwtw011123334455667 r. w m t e m m m g a t E 5 2581470369211111111111111.1111 fb r W u w u t a S 6 zaa maala .w 9 0 MM 0 m S g q SS E 2 333 4455 M R Vw w. .mmuwm mmhm R RD u U l d 8 b P .1 .1 a .1 H m Im H M a 0 25814703692 620 I v t h p v P n o o u m T uu a m a a asrewaemwamama at n H W m a S ..lb G 445567789901123 H a t e e e mi m M ddN mmmmmmmmmmm .mmm LLLLLLLLLLZZZZZ m d mm W n m m e I 4 25814703692 WI sd 0 e a a c a m D zssiasasara n .Ed wk .m O t. H a 0 m u R 22233344455MGM a mm a T m mm m m k m o O n b .1 e t. e h 0. u a O C T H t 0 T O 8t. W U C C C HM 25814703692 8 11%850000099999 & & r t 5 0 5 2333444555NB HHE UHHfl 1 .l. m mmmmmmmmmwm SIC E0 3 m 1 25814703692 M W t m m mmmaaaaanaua .1 of r. .1 n 36925814703692 m n ww flmw ww qge 0 mtfifiaaaaaammm m ......8.1....7.0.3.... M e r mmwmmwmmmmmwwmw Et %%%wuQ%% I amw te mw 36925814703692 R mmmm wmwmmmw W W H C a v v a v c J 4 pma m maamammmeawmmm m 2 E o I P 4 047047 037 W D E 1 222333444 L g 0 m BI) 005000000000000 I eet r m p umaawmawmaaaaa W 25814703692 m d maaaaaafiaasa .w. .m w f. m 11222333L44 3 wmm sssajsiaa fita A 1mmwmwwwwwmm Magma OOOMMM O MMMMMM M M E zamomlraoma/Toocli111115555500000 01H ttttttttttttttt T 11122233344. M 11111 W225814703692 I m m 70360. so izzzswamaama m mm mff P 4703692500147 wfi mM mmwmaaaame w 0 000000000000 E C 0 tttttttttttt u 470369258147 "h u m mnmwaaaaaaau m m m m m m t m n w m m m m m m B r. E HF L PF 0 n n n r n hm 6o B m o T m 1 T t T t T ta u t n n w m w u n 1 00000 0 l 0 l B B B WWm. 1 1 1112 2 Although Tables II through XI show the expected moisturerequired and the moisture required according to the present inventionfor percentages of oxygen enrichment from 1 to 5, which range of oxygenenrichment percentages may be economically obtained with presentlyavailable equipment, it is known that greater increases in ironproduction may be obtained by increasing the percentage of oxygenenrichment up to about 10%, for example, and it is expected that blastfurnaces will be operated in the future with such high percentages ofoxygen enrichment.

ranges of moisture that would be expected to be required and that wouldbe required according to the principles of the present invention forblast gas having an oxygen enrichment between 5% and 10% at temperaturesfrom 1100 F. to 2500 F.

shows that operation in accordance with the principles of the presentinvention, that is, at blast gas temperatures about 1400 F. to 1500 F.,makes it possible to obtain a reduction in required moisture of four percubic foot of blast gas, it is to be expected, as mentioned above, thatthe actual moisture saving will be greater especially at higherblastgastemperatures.

l l ods for taking full advantage of such auxiliary fuel additions sothat, in combination with reduced moisture additions, a smooth operatingfurnace is obtained, the coke-rate reduced, and the production rateincreased at substantial economic savings over conventional practice.

By auxiliary fuel additions is meant fuel introduced through the tuyeresor other than through the top of the furnace. As pointed out earlier,conventionally, limestone, ferrous bearing material, and carbonaceousmaterial such as coke are charged into the top of the furnace. Thecharge moves down the shaft of the fur nace and the coke, constitutingthe fuel of the mixture, is burned by the incoming blast to melt theiron producing molten pig iron. Auxiliary fuels, on the other hand, arenot introduced at the top of the furnace but near the bottom of thefurnace, preferably, in accordance with the invention, through the maintuyeres of the furnace and may include fuels such as natural gas, cokeoven gas, fuel oil, powdered carbonaceous materials such as coal, chator coke, or the products of combustion of these fuels.

The problems, economic and otherwise, of acquiring and using qualitycoke in blast furnace operations are Well known in the art. The economicsupplanting of quality blast furnace coke with auxiliary fuels is adesirable object. By supplying such auxiliary fules through the sides ofthe furnace, for example with the blast, the heat supplied through theblast is increased and it would ordinarily be expected that moistureadditions should be increased proportionally. However the complexreactions taking place within the furnace present problems of furnacecontrol, solution loss, and economic use of auxiliary fuels which, ithas been discovered dictate processes other than expected. In actualit afurnace being operated at high blast temperatures and reduced moistureadditions in accordance with the invention, must have the mositureadditions further reduced in order to economically use auxiliary fueladditions. That is, when a blast furnace is operated with blast gastemperature above about 1400-1500" F. and with auxiliary fuel additions,optimum results can only be obtained with aqueous additions less thanthe reduced additions set forth in Tables 11 to XI.

In explaining the invention, natural gas will be used as an example ofthe auxiliary fuel although the invention is not to be limited thereby.When adding natural gas to a blast furnace the following reactions arebelieved to have significance:

(1) CO -l-CQZCO C. 2C+O +2CO Consider the situation Where natural gas isadded prior to the tuyeres, for example burned in the wind prior to theblast furnace stoves. In such case the formula B above is applicablebecause the natural gas is burned with a surplus of oxygen and it addsheat to the blast plus the products of combustion CO and H moisture orits control equivalent is being added to the furnace when fuel is addedin this fashion. CO has the same thermodynamic effect as H O as itrequires heat to dissociate (see Formula 13(1) As pointed out earlier ithas been discovered that when making auxiliary fuel additions it isnecessary to operate the furnace at higher blast temperatures in orderto economically take advantage of the auxiliary fuel. When operating athigher blast temperatures the moisture additions are expected toincrease and normally would be increased to obtain a smooth operatingfurnace. Since fuel additions add moisture, or its control equivalent, asurplus of moisture results and the furnace runs cold. However, it hasbeen discovered that a blast furnace operated on moisture additions canbe operated with a precise and predeterminable reduction in moistureadditions to counteract the moisture and carbon dioxide produced byburning injectedfuel. By reducing the amount of moisture additions in anamount equivalent to the endothermic requirements of the products ofcombustion of injected fuel, it is possible to obtain the full economicbenefits of the auxiliary fuel in improved blast furnace operationsincluding reduction of the coke rate in accordance with the exothermicequivalents of the auxiliary fuel and the reducing agents added thereby.

The burning of auxiliary fuel in the blast presents certain problems,however. For one thing, the refractories in the blast furnace stoves andthe mains would have to be replaced in order to withstand the hightemperatures of the burning auxiliary fuel. With the extremely hightemperatures of the blast encountered heat losses are in reased beforethe blast reaches the furnace and yet the products of combustion of theauxiliary fuel would require additional heat once inside the furnace tobe dissociated and made available as reducing agents. Therefore,practically speaking, it has been discovered that it is moreeconomically feasible to add the natural gas, or other auxiliary fuel,at the tuyeres.

When adding the natural gas at the tuyeres the reaction set forth in Aabove can take place within the furnace. That is the auxiliary fuelburns in a shortage of oxygen and CO and H reducing agents, are formeddirectly. The question presented is what effect does this reaction haveon the endothermic requirements of auxiliary fuel additions. heatlosses, the endothermic requirements of auxiliary fuel additions areapproximately the same whether added at the tuyeres or burned prior tointroduction to the furnace. It is believed that the reason for thiscould be, quite simply, that the same reaction (B above) takes placeregardless of where the auxiliary fuel is added.

' Another explanation behind the endothermic equivalency could be thatwhen reaction A takes place with constant wind the addition of naturalgas at the tuyeres reduces the 0 available for the C reaction. Areduction in the C reaction reduces the heat available in the furnace,as this reaction is more exothermic than the A reaction since the cokeis already heated and inherently produces more heat in combustion. Thenatural gas, being gaseous, is more readily combustible and to someextent takes the place of coke combustion. Therefore even in the absenceof the formation of H 0 and CO the introduction of natural gas into thetuyeres produces the same overall effect as adding moisture in spite ofthe fact that neither H O nor CO may be formed. Therefore whether theauxiliary fuel is burned before entering the furnace or added at thetuyeres a reduction in moisture additions is required in proportion tothe products of combustion of auxiliary fuel when a like amount ofauxiliary fuel is burned in a surplusage of oxygen. However, theteachings of the invention emphasize the advantages of introducing theauxiliary fuel at the tuyeres, such as the avoidance of plant heatlosses.

Examples of blast furnace operations, using moisture additions forfurnace control, with and without auxiliary fuel additions, are includedin Table XVII to follow. The experimental data included therein areaverages of values obtained during the operation periods indicated. Theexperimental blast furnace employed has a hearth diameter of four feet,a height of approximately 26 feet, and a working volume of approximately305 cubic feet. Owing to the greater heat losses per unit of productionin an experimental furnace of this size, as compared to a commercialfurnace, higher blast temperatures are employed and must be convertedfor commercial furnace application based on established conversiontables recognized in the art as follows:

Experimental Furnace: Commercial Furnace, F.

1,600 P. 1,250 1,80() F. 1,425 2,100 P. 1,700 2,475 F. 2,000

It has been discovered that, disregarding plant.

TABLE XVII Example Example Example Example 1 2 3 4 FURNACE PERFORMANCEIron ProcL, Net Tons Per Day 18. 74 18.91 20.82 18. 31 Coke Rate, Lbs.Per Net 'Ion 1, 322 1, 006 1, 104 1, 105 Slag Volume, Lbs. Per Net Ton085 993 957 1, 005

OPERATING CONDITIONS Oxygen Enrichment Wind Rate, c.f.rn 800 800 800 800Moisture, Grains Per Cu. Ft. 27 6. 8 5.6 4 Gas Iniec. Bate, c.f.1n 4O 40Blast Temp, F 2, 475 2, 475 2, 475 2, 475 Top Temp, F 328 458 340 452nor METAL DATA Silicon, Percent 0.88 0.77 0.88 0.74 Sulfur, Percent. 0.039 0. 045 0. 031 0. 038 Temperature, F 2, 515 2, 490 2, 525 2, 499Number of Oasts 24 12 28 16 Hours of Operation 72 122 27 i It can beseen from the above data that the use of auxiliary fuel and high blasttemperatures brings about an increased metal production rate and adecreased coke rate. Additional coke savings are realized from thecarbon of the auxiliary fuel which replaces carbon from the burden coke.

An important discovery of the invention is that fuel additions cannot beeconomically used without increasing the blast temperature. Theproduction rate of a furnace will increase directly with auxiliary fueladditions if the cooling effect of the auxiliary fuel and aqueousadditions are compensated for by increased blast temperatures anddecreased aqueous additions. In practice, the necessary increase intemperature has amounted to about 120 F. for each percent of auxiliaryfuel (natural gas) added. The necessary increase in blast temperaturewith auxiliary fuels would not be as high as 120 F. with each percent ofauxiliary fuel addition if a more exothermic fuel than natural gas, suchas powdered coal, were used. Within the practical limits of blasttemperatures imposed at most blast furnace sites today the maximumpercentage of natural gas which could be effectively used would bearound 5 to 6% by volume of the blast. With more exothermic auxiliaryfuels the percentage may be increased to 8% or beyond.

' As pointed out earlier about one grain of moisture per cubic foot ofblast gas is added with each 30 increase in blast gas temperature. Foreach percent by volume natural gas added blast gas temperature should beincreased approximately 120. From this data it can be seen that, as faras blast furnace control is concerned, one percent of natural gas isapproximately equivalent, considering smooth operations, to four grainsof moisture. In other words, when making auxiliary fuel additions ofnatural gas, for each percent of natural gas added to the blast, theaqueous additions should be reduced approximately four grains.

The reduction in aqueous additions is not without limitation, however. Asignificant discovery, forming part of the invention, is that aqueousadditions should not be eliminated entirely. In practice, the furnacecannot be readily controlled by adjusting the rate of auxiliary fuelinjections, but excellent control can be obtained by maintaining someaqueous additions to the furnace.

The reasons why the auxiliary fuel is not effective in instantaneouscontrol, even though it serves as an equivalent in many other respectsto aqueous addition, are multiple and speculative. Mostly, theexplanations hinge on the change in the amount of carbon available inthe furnaces with changes in the auxiliary fuel injection rate. Considera furnace which is hanging and the area beneath abridge or scaffoldingcausing the furnace to hang is becoming increasingly hot. Ideally,aqueous additions or the moisture additions effect of adding auxiliaryfuel would serve to cool this area and lengthen the combustion zone inthe furnace and thereby reestablish smooth descent of the burden. Ingeneral, cooling of the hot zone takes place with either additive.However, due to the presence of carbon in the auxiliary fuel and thetendency of this carbon to combine with 0 more readily than the carbonin the coke, there is less coke burned. Descent of the burden will besluggish because of the lowered demand for burden carbon. On the otherhand, aqueous additions effect the necessary cooling and charge only 0or H into the furnace so that the burden starts to move more readily.Also, maintaining limited aqueous additions to the furnace permitstemperature control of the furnace affecting silicon and sulphur contentof the melt without adding carbon to the furnace.

In actual practice, the amount of aqueous additions maintained should besufficient to exercise furnace control. If dehumidifying equipment isnot used, aqueous additions of about 7 grains are suflicient to allowfor normal variations in the ambient atmospheric humidity and leave amargin for varying the aqueous addition to effect instantaneous control.If dehumidifying equipment is used on the blast, the aqueous additionsto the furnace helpful in instantaneous control can be maintained byregulating the humidity of the air used in the blast.

In summary, when using auxiliary fuel, to obtain an increased productionfrom a blast furnace, the blast gas temperature should be increased andthe aqueous additions reduced in accordance with the endothermicrequirements of the auxiliary fuel. The coke rate should be reduced inaccordance with the carbon and reducing agents added by the auxiliaryfuel. If oxygen enrichment is used the production rate will be increasedsince the consumption of the oxygen of the blast by the auxiliary fuelwill be reduced and will be available for burning additional coke in theburden and increasing the driving rate.

It is to be expressly understood that various changes and substitutionsmay be made in the specific embodiments described herein withoutdeparting from the spirit of the invention as well understood by thoseskilled in the art. Therefore, reference will be had to the appendedclaims for a definition of the limits of the invention.

I claim:

1. Method of operating a blast furnace in which iron bearing material issmelted and in which coke is burned, comprising the steps of formingblast gas including atmospheric air, enriching blast gas with oxygen,adding aqueous fluid to the blast gas, heating the blast gas to atemperature above about 1400 F. to 1500 F., and blowing blast gas intothe furnace, the oxygen enrichment being in the range of 1%-l0%, and thequantity of aqueous fluid in the blast gas being from about 12.2 toabout 82.2 grains of moisture per cubic foot of blast gas, the aqueousfluid in the blast gas increasing from about 12.2 to about 82.2

'1 55 grains of moisture per cubic foot of blast gas as the oxygenenrichment increases from about 1% to about 10%.

2. Method of operating a blast furnace in which iron bearing material issmelted and in which coke is burned, comprising the steps of formingblast gas including atmospheric air, enriching blast gas with oxygen,adding aqueous fluid to the blast gas, heating the blast gas to a temrperature above about 1400 F. to 1500 F., and blowing blast gas into thefurnace, the oxygen enrichment being in the range of 1%-5% and thequantity of aqueous fluid in the blast gas being from about 12.2 toabout 70.2 grains of moisture per cubic foot of blast gas, the aqueousfluid in the blast gas increasing from about 12.2 to about 70.2 grainsof moisture per cubic foot of blast gas as the oxygen enrichmentincreases from about 1% to about 5% l 3. Method of operating a blastfurnace in which iron bearing material is smelted and in which coke isburned, comprising the steps of forming blast gas including atmosphericair, enriching blast gas with oxygen, adding aqueous fluid to the blastgas, heating the blast gas to a temperature above about 1400 F. to about1500 F., and blowing blast gas into the furnace, the oxygen enrichmentbeing within the range of 5 and the quantity of aqueous fluid in theblast gas being from about 26.2 to about 82.2 grains of moisture percubic foot of blast gas, the aqueous fluid in the blast gas increasingfrom about 26.2 to about 82.2 grains of moisture per cubic foot of blastgas as the oxygen enrichment increases from about 5% to about 10%.

4. Method of operating a blast furnace in which iron bearing material issmelted and in which coke is burned, comprising the steps of formingblast gas including atmospheric air, enriching blast gas with oxygen,adding aqueous fluid to the blast gas, heating the blast gas to atemperature above about 1400 F, to 1500 F. and up to 2000 F., andblowing blast gas into the furnace, the oxygen enrichment being in therange of 1% to 10% and the quantity of aqueous fluid in the blast gasbeing from about 12.2 to about 65.7 grains of moisture per cubic foot ofblast gas, the aqueous fluid in the blast gas increasing from about 12.2to about 65.7 grains of moisture per cubir foot of blast gas as theoxygen enrichment increases from about 1% to about 10%.

5. Method of operating a blast furnace in which iron bearing material issmelted and in which cokeis burned, comprising the steps'of formingblast gas including atmospheric air, enriching blast gas with oxygen,adding aqueous fluid to the blast gas, heating the blast gas to atemperature above about 1400 F. to 1500 F. and up to about 2000 F., andblowing blast gas into the furnace, the oxygen enrichment in the blastgas being in the range of 1%5%, and the quantity of aqueous fluid in theblast gas being from about 12.2 to about 53.7 grains of moisture percubic foot of blast gas, the aqueous fluid in the blast gas increasingfrom about 12.2 to about 53.7 grains of moisture per cubic foot of blastgas as the oxygen enrichment increases from about 1% to about 5%.

6. Method of'operating a blast furnace in which iron bearing material issmelted and in which coke is burned, comprising the steps of formingblast gas including atmospheric air, enriching the blast gas withoxygen, adding aqueous fluid to the blast gas, heating the blast gas toa temperature above about 1400 F. to 1500 F. and up to about 2000 F.,and blowing the blast gas into the furnace, the oxygen enrichment beingwithin the range of about 5%l0%, and the quantity of aqueous fluid inthe blast gas being from about 26.2 to 65.7 grains of moisture per cubicfoot of blast gas, the aqueous fluid bearing material is smelted and inwhich coke is burned, comprising the steps of forming blast gasincluding atmospheric air, enriching blast gas with oxygen, addingaqueous fluid to the blast gas, heating the blast gas to a temperatureabove about 2000 F. and up to about 2500 F, and blowing blast gas intothe furnace, the oxygen enrichment in the blast gas being in the rangeof l%l0%, and the quantity of aqueous fluid in the blast gas being fromabout 28.7 to about 82.2 grains of moisture per cubic foot of blast gas,the aqueous fluid in the blast gas increasing from about 28.7 to about82.2 grains of moisture per cubic foot of blast gas as the oxygenenrichment increases from about 1% to about 10%.

8. Method of operating a blast furnace in which iron.

bearing material is smelted and in which coke is burned, comprising thesteps of forming blast gas including atmospheric air, enriching blastgas with oxygen, adding aqueous fluid to the blast gas, heating theblast gas to a temperature above about 2000 F. and up to about 2500 F.,and blowing blast gas into the furnace, the oxygen enrichment in theblast gas being in the range of 1%5%, and the quantity of aqueous fluidin the blast gas being from about 28.7 to about 70.2 grains of moistureper cubic foot of blast gas, the aqueous fluid in the blast gasincreasing from about 28.7 to about 70.2 grains of moisture per cubicfoot of blast gas as the oxygen enrich ment increases from about 1% toabout 5%.

9. Method of operating a blast furnace in which iron bearing material issmelted and in which coke is burned, comprising the steps of formingblast gas including atmospheric air, enriching blast gas with oxygen,adding aqueous fluid to the blast gas, heating the blast gas to atemperature above about 2000 F. and up to about 2500 F., and blowingblast gas into the'furnace, the oxygen enrichment being within the rangeof 5%l0%, and the quantity of aqueous fluid in the blast gas being fromabout 42.7 to about 82.2 grains of moisture per cubic foot of blast gas,the aqueous fluid in the blast gas increasing from about 42.7 to about82.2 grains of moisture per cubic foot of blast gas as the oxygenenrichment increases from about 5% to about 10%.

10. Method of operating a blast furnace in which iron bearing andcarbonaceous material are charged into the top of the furnace and ablast gas is introduced into the bottom of the furnace comprising thesteps of preheating the blast gas to a temperature above about 1400 F.,and adding aqueous fluid to the blast gas in accordance with thetemperature of the blast gas, the quantity of aqueous fluid added beingabout nine grains of aqueous fluid per cubic foot of blast furnace gasat a temperature of about 1400 F. with about three grains of moistureper cubic foot of blast gas required'to be added with each F. increasein blast gas temperature above 11. Method of operating a blast furnacein'which iron hearing and carbonaceous materials are charged into thetop of the furnace and a blast gas is introduced into the bottom of thefurnace comprising the steps of preheating the blast gas to temperaturesabove 1400 5., adding aqueous fluid to the blast gas with about 9 grainsof aqueous fluid per cubic foot of blast gas being added at 1400 F.,adding auxiliary fuel to the blast gas in the range of about 1% to about8% by volume of the blast gas, and controlling the blast gas temperaturein accordance with the formula, blast gas temperature: 1400+(M)33 F.+(F)F, wherein M is equal to the grains of aqueous fluid above 9 grains percubic foot of blast gas added and F is equal to the percentage of theblast gas by volume auxiliary fuel added to the blast gas.

12. In a process of heating and humidifying the'blast for ametallurgical blast furnace, which comprises: blowing cold blast air forthe blast of the furnace through a preheating medium therefor andthereby preheating the blast for the furnace, thereafter augmenting theheat of the blast from said medium by burning combustible fuel with partof the total air of the blast directly in the preheated blast, andthereafter delivering the heat augmented hot blast into the hearth inthe blast furnace While charged with Water vapor to a predeterminedconstancy of humidity, the improvement comprising the steps of;effecting said augmenting of the heat of the blast by burning a hydrogencontaining fuel as the combustible fuel directly in the blast andthereby charging the blast with a substantial part of the water vaporfor said predetermined constancy of humidity as a product of saidcombustion, and adding the remainder of the total amount of vapor toform said predetermined constancy of humidity in the form of aqueousfluid to the blast before the heat of the blast is augmented.

13. A process as claimed in claim 12, and in which the preheating by theaforesaid preheating medium is effected by regenerative heating of theblast by heat previously stored in heat storing material.

14. A method as claimed in claim 12, and in which the amounts of thehydrogen containing gas that is burned as aforesaid, and of the part ofthe total air of the blast that is burned with the gas, is controlledby, and in accordance with variations in the total amount of cold blastair blown in the first aforesaid blowing step for the blast.

15. Method of operating a blast furnace in which iron bearing materialand carbonaceous material are charged into the top of the furnace andblast gas is introduced at the bottom of the furnace, comprising thesteps of preheating the blast gas to a predetermined temperature, addingauxiliary fuel to the blast gas, and adding aqueous fluid to the blastgas in accordance with the temperature of the blast gas and theendothermic requirements of the auxiliary fuel, the quantity of aqueousfluid being substantially equal to the aqueous fluid required at thepredetermined temperature without auxiliary fuel being introduced intothe furnace and a quantity of aqueous fluid equivalent to theendothermic requirements of the auxiliary fuel, the quantity of aqueousfluid required to be added to the blast gas at the predeterminedtemperature being from about 9 grains per cubic foot of blast gas at atemperature of about 1400 F. with about 3 grains of aqueous fluid percubic foot of blast gas required to be added for each 100 F. increase inblast gas temperature above 1400 F.

16. The method of operating a blast furnace as defined in claim 15including the step of controlling the quantity of carbonaceous materialcharged into the top of the blast furnace based on the exothermicequivalent of the auxiliary fuel added to the blast gas.

17. The method of operating a blast furnace as defined in claim 15 inwhich the auxiliary fuel comprises natural gas added in the range ofabout 1 percent to about 8 percent by volume of the blast gas.

18. Method of operating a blast furnace in which iron bearing materialand carbonaceous material are charged into the top of the furnace andblast gas is introduced through blast furnace tuyeres at the bottom ofthe furnace comprising the steps of preheating the blast gas to apredetermined temperature, adding aqueous fluid to the blast gas, addingauxiliary fuel at the blast furnace tuyeres, and controlling the aqueousfluid additions to the blast gas in accordance with the temperature ofthe blast gas and the endothermic requirements of the auxiliary fuel,the quantity of aqueous fluid additions being substantially equal to theaqueous fluid required at the predetermined blast gas temperature offsetby equivalent aqueous fluid substantially equal to the endothermicrequirements of the added auxiliary fuel, the quantity of aqueous fluidrequired at the predetermined blast gas temperature being approximately9 grains per cubic foot of blast gas at a temperature of about 1400 F.with 3 grains of aqueous additions per cubic foot of blast gas beingadded for each 100 F. increase in blast gas temperature above 1400 F.

19. Method of operating a blast furnace in which iron bearing materialand carbonaceous material are charged into the top of the furnace andblast gas is introduced into the bottom of the furnace comprising thesteps of preheating the blast gas to a predetermined temperature, addingauxiliary fuel to the blast gas, and adding aqueous fluid to the blastgas in accordance with the temperature of the blast gas and theendothermic requirements of the auxiliary fuel, the quantity of aqueousfluid added to the blast gas being substantially equal to the differencebetween the quantity of aqueous fluid required to be added to blast gasat the predetermined temperature without auxiliary fuel being introducedinto the furnace and a quantity of aqueous fluid equivalent to theendothermic requirements of the auxiliary fuel, the quantity of aqueousfluid required to be added to the blast gas without auxiliary fuelintroduced into the furnace varying between about 9 grains of aqueousfluid per cubic foot of blast gas at 1400 F. and about 45 grains ofaqueous fluid per cubic foot of blast gas at 2500 F.

20. Method of operating a blast furnace in which iron bearing materialand carbonaceous material are charged into the top of the furnace andblast gas is introduced into the bottom of the furnace comprising thesteps of preheating the blast gas to a predetermined temperature,enriching the blast gas with a predetermined percentage of oxygen, inthe range of about 1% to about 10% of the blast gas, adding auxiliaryfuel to the blast gas, and adding aqueous fluid to the blast gas inaccordance with the temperature of the blast gas, the percent of oxygenenrichment and the endothermic requirements of the auxiliary fuel, thequantity of aqueous fluid added to the blast gas being substantiallyequal to the difference between the quantity of aqueous fluid requiredto be added to blast gas at the predetermined temperature and thepredetermined percentage of oxygen enrichment without auxiliary fuelintroduced into the furnace and the quantity of aqueous fluid equivalentto the endothermic requirements of the auxiliary fuel, the quantity ofaqueous fluid required to be added to the blast gas without auxiliaryfuel introduced into the furnace varying between about 12 grains ofaqueous fluid per cubic foot of blast gas at 1500 F. and 1% oxygenenrichment and about 82 grains of aqueout fluid per cubic foot of blastgas at 2500 F. and about 10% oxygen enrichment.

21. Method of operating a blast furnace in which iron bearing materialand carbonaceous material are charged into the top of the furnace andblast gas is introduced into the bottom of the furnace comprising thesteps of preheating the blast gas to a predetermined temperature, addingnatural gas to the blast gas in the range of about 1 percent to about 6percent by volume of the blast gas, and adding aqueous fluid to theblast gas in accordance with the temperature of the blast gas and theendothermic requirements of the auxiliary fuel, the quantity of theaqueous fluid additions being equal to the aqueous fluid additionsrequired at the predetermined blast gas temperature offset by equivalentaqueous fluid substantially equal to the endothermic requirements of theadded natural gas, the quantity of aqueous fluid additions required bythe blast gas temperature being equal to approximately 9 grains percubic foot of blast gas at a temperature of about 1400 F. with about 3grains of aqueous additions per cubic foot of blast gas being added foreach F. increase in blast temperature above 1400 F. and the equivalentaqueous fluid for the natural gas added being approximately 4 grains ofaqueous fluid for each percent by volume of natural gas added to theblast gas.

22. In the operation of a blast furnace in which iron bearing materialand carbonaceous material are charged into the top of the furnace andblast gas is introduced at the bottom of the furnace, a method forincreasing the production rate of the furnace comprising the steps ofadding natural gas to the blast gas in the range of about 1 percent toabout 8 percent by volume of the blast gas, and controlling the blastgas temperature in accordance 19 with the endothermic requirements ofthe added natural gas, the endothermic requirements being an increase inblast gas temperature of about 120 F. for each percent by volume ofnatural gas added to the blast gas.

23. Method of operating a blast furnace in which iron bearing materialand carbonaceous material are charged into the top of the furnace and ablast gas is introduced at the bottom of the furnace, comprising thesteps of preheating the blast gas to a predetermined temperature,introducing material into the bottom of the'furnace as auxiliary fuel,and adding aqueous fluid to the blast gas in accordance with thetemperature of the blast gas and the endothermic requirements of theintroduced material, the quantity of aqueous fluid added to the blastgas being substantially equal to the difference between the quantity ofaqueous fluid required to be added to the blast gas at the predeterminedtemperature Without auxiliary fuel being introduced into the furnace anda quantity of aqueous fluid equivalent to the endothermic requirementsof the introduced material, the predetermined temperature of the blastgas being from about 1400 F. and up to about 2500" F. and the quantityof aqueous fluid required to be added to the blast gas at thepredetermined temperature being from about 9 grains of moisture up toabout 45 grains of moisture per cubic foot of blast gas, and thequantity of aqueous fiuid equivalent to the endothermic requirements ofthe introduced material being approximately 4 grains of aqueous fluidper cubic foot of blast gas per endothermic requirement N, theendothermic requirement N being equal to the endothermic requirement ofa quantity of natural gas equal to 1% of the blast gas.

References Eited by the Examiner UNITED STATES PATENTS 1,510,271 9/1924Gottschalk 75--41 2,219,046 10/ 1940 Koller et al. 7542 2,715,575 8/1955Coutant 75-41 2,719,083 9/1955 Pomykala 75-42 2,729,555 1/1956 Shipley75-41 2,735,758 2/1956 Strassburger 7541 2,778,018 1/1957 Strassburger75-41 X OTHER REFERENCES Blast Furnace Proceedings, 1958, vol. 17, pages4-39.

Iron Age, vol. 184, July 16, 1959, "rages 104 and 105 relied on.

Journal of Metals, January 1961, pages 25-30 (also Blast FurnaceProceeding, vol. 19, 1960, pages 238-278).

Metal Progress, August 1949 (pp. 234 and 236 relied on). a

Steel, vol. 139, No. 22, Nov. 26, 1956, pages 98, 101, 104, 107, and 110relied on.

Sweetser, Blast Furnace Practice, 1st Edition, 1938,

McGraw-Hill Book Co., Inc, New York (page 253 relied,

DAVID L. RECK, Primary Examiner.

RAY K. WlNDHAM, ROGER L. CAMPBELL,

Examiners.

1. METHOD OF OPERATING A BLAST FURNACE IN WHICH IRON BEARING MATERIAL ISSMELTED AND IN WHICH COKE IS BURNED, COMPRISING THE STEPS OF FORMINGBLAST GAS INCLUDING ATMOSPHERIC AIR, ENRICHING BLAST GAS WITH OXYGEN,ADDING AQUEOUS FLUID T THE BLAST GAS, HEATING THE BLAST GAS TO ATEMPERATURE ABOVE ABOUT 1400*F. TO 1500*F., AND BLOWING BLAST GAS INTOTHE FURNACE, THE OXYGEN ENRICHMENT BEING IN THE RANGE OF 1%-10%, AND THEQUANTITY OF AQUEOUS FLUID IN THE BLAST GAS BEING FROM ABOUT 12.2 TOABOUT 82.2 GRAINS OF MOISTURE PER CUBIC FOOT OF BLAST GAS, THE AQUEOUSFLUID IN THE BLAST GAS INCREASING FROM ABUT 12.2 TO ABOUT 82.2 GRAINS OFMOISTURE PER CUBIC FOOT OF BLAST GAS AS THE OXYGEN ENRICHMENT INCREASESFROM ABOUT 1% TO ABOUT 10%.